David's Whizzy Periodic Table
Applet-based table with visualizations of the electron shell model, the nucleus, the visual emission spectrum, and energy levels of the electrons. Also has interesting facts about each element represented. [Java required]
http://www.colorado.edu/physics/2000/applets/a2.html

Earth Scientist's Periodic Table
Nontraditional periodic table organized by charge. Designed to show trends in the natural sciences of geochemistry, mineralogy, and aqueous chemistry.
http://www.gly.uga.edu/railsback/PT.html

EnvironmentalChemistry.com: Periodic Table of Elements
&#x005B;Very comprehensive data, write-ups, extensive listing of nuclides] Data on elements includes scores of properties, element names in a dozen languages and almost all known nuclides. Environmental chemistry articles round out site.
http://environmentalchemistry.com/yogi/periodic/

ePeriodicTable
An interactive and clickable periodic table of the elements, which contains basic element properties and descriptions.
http://www.eperiodictable.com/

Exploring the Table of Isotopes
&#x005B;Nuclide data only, extensive listing of nuclides] Provides isotope data for almost all known nuclides. From Berkeley Laboratory.
http://ie.lbl.gov/education/isotopes.htm

On-line The Periodic Table of Elements
&#x005B;Basic data, requires JavaScript] Includes historical information about the elements in Italian, but the table itself is in English.
http://www.themeter.net/elemen_e.htm

The Periodic Table
Features an interactive table based on the IOUPAC 1985 standard.
http://www.periodic-table.org.uk/

The Periodic Table Challenge
&#x005B;No element data] An auto-scored blank periodic table. The user fills it in online and the score is returned automatically.
http://www.ilpi.com/genchem/periodicquiz.html

Periodic Table of Elements
&#x005B;Basic data] Chemistrydata.com offers very basic information about elements in a searchable format. Includes a printable periodic table.
http://www.chemistrydata.com/

Periodic Table of Elements
&#x005B;Detailed] Includes general information about an element, atomic number and weight, shells and filling orbital, melting and boiling point, covalent and atomic radius, and lots of other parameters.
http://atlas.chemistry.uoc.gr/ptoe/

Periodic Table of Parameters
&#x005B;Basic] This table lists and describes some well documented and validated parameter sets available for modeling each element by Molecular Mechanics and Quantum Mechanics molecular modeling methods.
http://www.chamotlabs.com/Freebies/Table/parameters-table.html

Periodic Table of the Elements
&#x005B;Basic data, includes printable version] Information on each of the chemical elements and data on their properties. Some site information is only in Czech language.
http://www.tabulka.cz/english/

The Pictorial Periodic Table
&#x005B;Basic data, very basic writeups, some pictures] Includes a printable periodic table, a cross-referenced list of nuclides, alternate styles, history, references, and many links to periodic table resources on the web.
http://dwb.unl.edu/Teacher/NSF/C04/C04Links/chemlab.pc.maricopa.edu/periodic/periodic.html

Table of the Nuclides
&#x005B;Nuclide data only, very extensive listing of nuclides] Map of all known nuclides, with their atomic mass, radioactive decay modes and half-lives, and related information. Brookhaven National Laboratory.
http://atom.kaeri.re.kr/

WebElements
&#x005B;Very comprehensive, includes very detailed write ups, basic nuclide data, extensive graphics] Professional scientists and students at school will all find something useful. Includes thousands of images relating to periodicity and structure.
http://www.webelements.com/

The Wooden 'Periodic Table' Table
&#x005B;Basic data] Based on a wooden 'periodic table' table. Contains photographs of over 200 element samples, with descriptions, experiments, and stories about many of them. Winner of the 2002 Ig Nobel prize in Chemistry.
http://www.theodoregray.com/PeriodicTable/